Seized Adjustment Ring on Rockford PTO Clutch

[rossaroni]

Had a slipping clutch on a tub grinder, and went to adjust it....found out that the locking tab was never engaged on the adjustment ring. Now I cant get the thing to move one way or another to try to adjust it.
Any advice on breaking this thing loose?

 

[mitch504]

an air hammer with a dull chisel in it

 

[kshansen]

an air hammer with a dull chisel in it

Along with a little penetrating oil in the area of the threads.

 

[rossaroni]

Thanks, Gentlemen.
Tried the air hammer alone, no luck. Actually broke off a tooth on the ring. The water pump went on the tub as well, so while fixing that, I continually soaked the threads with 2 cans of PB. By the time I had everything back together on the pump, the clutch was willing to cooperate.
There's days where I hate being my own mechanic, but man, do I like not seeing a bill from someone else that is